Three patients from the Klaus Ross Centre for Alternative Cancer Treatment in Brüggen-Bracht, North Rhine-Westphalia died over three consecutive days: a 55-year-old Belgian woman, a 55-year-old Dutch man and a 43-year-old Dutch woman.
Two further patients are currently in a Dutch hospital, police reported.
The 43-year-old woman with breast cancer had been the first to report symptoms after receiving treatment on July 25th, complaining of headaches and later losing the ability to speak.
However, the "cause of her death remains unclear," German prosecutors said in a statement earlier this week.
According to Tagesspiegel, like the majority of the clinic's patients, the deceased all came from Belgium and the Netherlands, where alternative therapies are more strictly regulated than in Germany.
The alternative cancer treatment centre. Photo: DPA
The clinic, close to the Dutch border, reported the unexpected death of the Dutch woman in a statement on its website, saying "we regret this seriously and are in shock as we heard the news." It has not updated its statement with information about the other two deaths.
The Klaus Ross clinic added that any suggestion by the media that the alternative medicine treatment could be responsible was "unfounded".
"Alternative medicine is always an extra tool to battle diseases," said the clinic, adding that it always advised patients to be monitored by their own doctors.
"We believe 100 percent in our philosophy, treatments and passion to keep offering our best service to those who need it most."
However, German prosecutors have said that while medical investigations are ongoing into the cause of the deaths, there is a "concrete health risk" for anyone who has been treated at the clinic and urged any patients showing any symptoms to "urgently seek medical advice". Dutch police also appealed for previous patients to report to the police with any information.
The centre's treatments include cancer therapy, pain-reducing therapy and drug addiction treatment. A ten-week course of treatment for cancer sufferers costs almost €10,000.